In gas turbine engines with axial flow compressors it is often necessary to transfer the fluid leaving the downstream end of one axial flow compressor at a first radial position to the upstream end of another axial flow compressor at a second radial position. The transfer of the fluid is usually achieved by locating a "swan necked" duct between the two axial flow compressors when there is sufficient axial space to do so. It is also often necessary to transfer the fluid leaving the downstream end of one axial flow compressor at a first radial position to an intercooler at a second radial position. The intercooler then supplies the cooled fluid to another axial flow compressor. The transfer of fluid from the first axial flow compressor to the intercooler is usually achieved by a "swan neck" duct.
However, where there is insufficient axial space to locate a "swan necked" duct the fluid must be transferred in some other way. If the fluid is transferred radially the pressure recovery in such a confined axial distance would very quickly overcome the momentum of the fluid flow and would produce excessive boundary layer growth and large areas of flow reversal.